Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$248.68	10.309%	$274.3164	$274.32	$274.30	$274.30
Purchase #2	$39.76	5.375%	$41.8971	$41.90	$41.90	$41.90
Purchase #3	$48.75	10.385%	$53.8127	$53.81	$53.80	$53.80
Purchase #4	$218.39	12.477%	$245.6385	$245.64	$245.65	$245.60
Purchase #5	$64.76	4.729%	$67.8225	$67.82	$67.80	$67.80
Purchase #6	$232.83	6.700%	$248.4296	$248.43	$248.45	$248.40
Purchase #7	$34.35	6.446%	$36.5642	$36.56	$36.55	$36.60
7 purchase totals =	$887.52		$968.4810	$968.48	$968.45	$968.40